In the production of L-lysine by fermentation, strains isolated from nature or artificial mutants thereof have conventionally been used in order to improve the productivity. Many artificial mutant strains that produce L-lysine are known, and many of them are S-2-aminoethylcysteine (AEC) resistant strains and belong to the genus Brevibacterium, Corynebacterium, Bacillus or Escherichia. Further, various techniques have been disclosed for increasing the amino acid production, for example, use of a transformant obtained by using recombinant DNA.
As for Escherichia bacteria, for example, methods for producing L-lysine by using a strain in which dihydrodipicolinate synthase (DDPS) activity is enhanced have been disclosed in Japanese Patent Application Laid-open (Kokai) No. 56-18596, U.S. Pat. No. 4,346,170 and Applied Microbiology and Biotechnology, 15, pp. 227-331 (1982). Further, a method for producing L-lysine by using an Escherichia bacterium into which DDPS derived form a Corynebacterium bacterium is introduced has been disclosed in Korean Patent Publication No. 92-8382. Furthermore, a method for producing L-lysine using a strain which is transformed with a plasmid containing DNA that codes for dihydrodipicolinate synthase derived from an Escherichia bacterium having a mutation for desensitizing feedback inhibition by L-lysine, DNA that codes for aspartokinase of which feedback inhibition by L-lysine is desensitized, DNA that codes for dihydrodipicolinate reductase, and DNA that codes for diaminopimelate dehydrogenase derived from a coryneform bacterium is disclosed in International Publication No. WO95/16042.
As for Brevibacterium bacteria, International Publication No. WO95/11985 discloses that L-lysine productivity can be improved by enhancement of the activity of intracellular nicotinamide adenine dinucleotide transhydrogenase. Further, a method for producing L-lysine using a strain in which phosphoenolpyruvate carboxylase activity is solely enhanced and a method for producing L-lysine using a strain in which aspartate-semialdehyde dehydrogenase activity is solely enhanced are disclosed in Japanese Patent Application Laid-open No. 60-87788 and Japanese Patent Publication (Kokoku) No. 6-102028, respectively.
In the industrial production of amino acids by fermentation, the production is performed in a large scale. Therefore, even improvement in the yield of several percents may provide significant industrial value, and thus improvement of the yield is desired irrespective of the degree of the improvement.